A typical disk brake system of a vehicle includes a caliper with one or more pistons that hydraulically force brake pads toward one another and into contact with a rotor that spins relative to the caliper when the vehicle is moving. The pads have a high coefficient of friction so that when they are forced into contact with the spinning rotor during braking, the speed at which the rotor is spinning is decreased by the frictional contact between the pad and the rotor. As the rotor speed decreases, the kinetic energy of the rotor is converted into heat. Substantial amounts of heat can be generated in the brake pads. Brake pad temperatures can reach well over the melting point of aluminum, greater than about 600 degrees Celsius. Many different techniques or mechanisms are used to remove heat from the disk brake system through the rotor. An example of one mechanism is to provide an integral vent in the rotor through which ambient air moves when the rotor is spinning to cool the rotor. Prior to the present invention, heat was usually primarily removed from the brake pads through contact with the rotor, and through the brake fluid and the brake caliper via the hydraulic pistons.
The lack of a good thermal sink for the brake pad can lead to significant problems in some instances. One problem that arises when brake pads get hot is a condition in which the heat from the pad is conducted through the caliper piston to the brake fluid and causes the fluid to boil. Heat conducted through the caliper piston to the brake fluid can also lead to damaged brake caliper seals or warped caliper pistons. Another problem is a condition in which the brake pads get hot enough that they vaporize on contact with the rotor. In this condition, a cushion of gas is produced between the pad and the rotor which prevents the pad from contacting the rotor. Both of the above conditions lead to a decrease in brake efficiency which is also called fade. In extreme cases, the above conditions can result in a complete failure of the brake system.
Prior attempts have been made to address the problems arising from excessive heat in the brake pad and several patents have been issued which relate to cooling disk brake systems. However, these patents generally depend on the manufacture of specifically designed custom calipers or rotors that replace or modify the original equipment calipers on the vehicle. Examples of patents which require specially manufactured custom calipers are U.S. Pat. No. 5,002,160 and U.S. Pat. No. 6,446,766.
The '160 patent discloses a brake caliper that is specially manufactured to have a ventilation channel for ducting ambient air to a position between the brake pad backing plate and the piston of the caliper. Someone wishing to utilize the disk brake system disclosed in the '160 patent for cooling their brake pads would have to replace their calipers with the calipers disclosed in the '160 patent. Since the calipers are the most expensive component of the brake system, replacing the calipers with the specially manufactured calipers of the '160 patent is likely to be an expensive proposition.
The '766 patent discloses a specially constructed brake caliper which includes a duct that is formed inside of the body of the caliper. The duct is designed to direct air to a series of specially constructed hydraulic pistons. The pistons each have a radiator element through which the air from the duct flows to dissipate heat. The '766 patent is an example of a type of device which relies on a modified caliper and modified hydraulic pistons in an attempt to cool the brake pads. Specially constructing the caliper with air flow ducts adds to the complexity of the caliper and most likely also adds to the cost of manufacturing the caliper as well. In addition to the added cost of the caliper, the device described in the '766 patent also requires the hydraulic pistons to have radiator elements which would also have to be specially manufactured thereby increasing the cost of the device even further.
Other U.S. patents also require modified calipers in attempts to cool the brake pads in a disk brake system. What is needed is an effective disk brake pad cooling system which can be economically utilized without modifying or replacing expensive existing brake system components.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon reading of the specification and a study of the drawings.